use super::noop::NoopConsumer;

use super::plumbing::*;

use super::*;

/// `Skip` is an iterator that skips over the first `n` elements.

/// This struct is created by the [`skip()`] method on [`IndexedParallelIterator`]

///

/// [`skip()`]: trait.IndexedParallelIterator.html#method.skip

/// [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html

#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]

#[derive(Debug, Clone)]

pub struct Skip<I> {

    base: I,

    n: usize,

}

impl<I> Skip<I>

where

    I: IndexedParallelIterator,

{

    /// Creates a new `Skip` iterator.

    pub(super) fn new(base: I, n: usize) -> Self {

        let n = Ord::min(base.len(), n);

        Skip { base, n }

    }

}

impl<I> ParallelIterator for Skip<I>

where

    I: IndexedParallelIterator,

{

    type Item = I::Item;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result

    where

        C: UnindexedConsumer<Self::Item>,

    {

        bridge(self, consumer)

    }

    fn opt_len(&self) -> Option<usize> {

        Some(self.len())

    }

}

impl<I> IndexedParallelIterator for Skip<I>

where

    I: IndexedParallelIterator,

{

    fn len(&self) -> usize {

        self.base.len() - self.n

    }

    fn drive<C: Consumer<Self::Item>>(self, consumer: C) -> C::Result {

        bridge(self, consumer)

    }

    fn with_producer<CB>(self, callback: CB) -> CB::Output

    where

        CB: ProducerCallback<Self::Item>,

    {

        return self.base.with_producer(Callback {

            callback,

            n: self.n,

        });

        struct Callback<CB> {

            callback: CB,

            n: usize,

        }

        impl<T, CB> ProducerCallback<T> for Callback<CB>

        where

            CB: ProducerCallback<T>,

        {

            type Output = CB::Output;

            fn callback<P>(self, base: P) -> CB::Output

            where

                P: Producer<Item = T>,

            {

                crate::in_place_scope(|scope| {

                    let Self { callback, n } = self;

                    let (before_skip, after_skip) = base.split_at(n);

                    // Run the skipped part separately for side effects.

                    // We'll still get any panics propagated back by the scope.

                    scope.spawn(move |_| bridge_producer_consumer(n, before_skip, NoopConsumer));

                    callback.callback(after_skip)

                })

            }

        }

    }

}